extends Node
## Weather model: what the sky is doing right now, and what that means for
## warmth, wetness and light. Visuals and sound live in weather_fx.gd.
##
## Deterministic: the weather at any moment is a function of the world seed and
## the absolute world time (day + time of day), so saves don't store it and in
## M2 every client can compute the same weather as the server.
##
## A slow 1D noise "front" value picks the state: high = clear, low = rain,
## lowest = storm. About one day in four is a cold day, when rain falls as snow
## (and a storm becomes a blizzard). Above the snowline it always snows.
## Outputs ease toward the state's targets over about a minute, so fronts
## roll in rather than switching.
##
## P4 (docs/PROGRESSION_DESIGN.md §5): every 12 days a hard winter, three
## bitter cold days in a row (hard_winter()), colder still, with more snow and
## blizzards. A blizzard cuts visibility right down and its wind strips the
## warmth from anyone out in it (blizzard_chill(); a shelter keeps it out).

signal state_changed(state: String)

const STATES := ["clear", "cloudy", "rain", "storm", "snow", "blizzard"]
## Thresholds on the front value (see _state_for). Tuned with
## tests/test_weather_building.gd so that over many days it's roughly
## clear 40%, cloudy 30%, rain 20%, storm 10%.
var cut_cloudy := 0.07
var cut_rain := -0.19
var cut_storm := -0.42

## Per-state targets: clouds 0..1, precip 0..1, wind 0..1, light (sun/ambient
## multiplier), fog (density multiplier), warmth (added to air warmth).
const TARGETS := {
	"clear":    {"clouds": 0.30, "precip": 0.0, "wind": 0.25, "light": 1.00, "fog": 1.0, "warmth": 0.0},
	"cloudy":   {"clouds": 0.72, "precip": 0.0, "wind": 0.45, "light": 0.72, "fog": 1.4, "warmth": -3.0},
	"rain":     {"clouds": 0.92, "precip": 0.6, "wind": 0.60, "light": 0.50, "fog": 2.2, "warmth": -6.0},
	"storm":    {"clouds": 1.00, "precip": 1.0, "wind": 1.00, "light": 0.30, "fog": 3.0, "warmth": -12.0},
	"snow":     {"clouds": 0.90, "precip": 0.6, "wind": 0.35, "light": 0.68, "fog": 2.6, "warmth": -14.0},
	"blizzard": {"clouds": 1.00, "precip": 1.0, "wind": 1.00, "light": 0.40, "fog": 7.0, "warmth": -24.0},
}
const COLD_DAY_WARMTH := -8.0
const BLEND_SECONDS := 50.0      ## time for outputs to cross from one state to another
const CALM_START := 600.0        ## a new world's first 10 minutes are always clear
const COLD_DAY_CHANCE := 0.25
const HARD_WINTER_EVERY := 12     ## days 12-14, 24-26, ...
const HARD_WINTER_DAYS := 3
const HARD_WINTER_WARMTH := -8.0  ## on top of a cold day's
const BLIZZARD_CHILL := 18.0      ## more warmth lost out in a blizzard's wind (a hard winter's freezes you by day)
## In a hard winter the weather leans wet (more snow and blizzards).
const HARD_WINTER_FRONT := -0.18

var world_seed := 1337
var day_night: Node
var snowline := 32.0             ## above this height precipitation is snow
var frozen := false              ## title-screen backdrop: hold clear weather
var override := ""               ## force a state (tests, screenshots); "" = natural

var state := "clear"
var cold_day := false
# Smoothed outputs.
var clouds := 0.3
var precip := 0.0
var wind := 0.25
var light := 1.0
var fog := 1.0
var warmth := 0.0
var ground_wet := 0.0            ## 0..1 how soaked the ground looks
var snow_cover := 0.0            ## 0..1 how much snow has settled
var flash := 0.0                 ## lightning brightness, decays fast
var lightning_count := 0

var _noise := FastNoiseLite.new()
var _strike_left := 8.0
var _rng := RandomNumberGenerator.new()

func setup(seed: int, dn: Node) -> void:
	world_seed = seed
	day_night = dn
	_noise.seed = seed + 401
	_noise.noise_type = FastNoiseLite.TYPE_SIMPLEX_SMOOTH
	_noise.frequency = 1.0 / 900.0     # a wet spell lasts about 6 minutes
	_noise.fractal_type = FastNoiseLite.FRACTAL_FBM
	_noise.fractal_octaves = 2
	_rng.seed = seed + 402
	snap()

## Seconds since the world began (day 1, 00:00).
func world_seconds() -> float:
	return (float(day_night.day - 1) + float(day_night.time)) * float(day_night.day_length)

## Day `day` is one of a hard winter's three bitter days.
static func hard_winter(day: int) -> bool:
	return day >= HARD_WINTER_EVERY and (day - HARD_WINTER_EVERY) % HARD_WINTER_EVERY < HARD_WINTER_DAYS

## The first day of the next hard winter on or after `day`.
static func next_hard_winter(day: int) -> int:
	var d := maxi(day, HARD_WINTER_EVERY)
	while not hard_winter(d):
		d += 1
	return d

func is_cold_day(day: int) -> bool:
	if day <= 1:
		return false
	if hard_winter(day):
		return true
	return float(absi(hash(Vector2i(world_seed, day))) % 10000) / 10000.0 < COLD_DAY_CHANCE

## The raw front value at an absolute time (higher = fairer).
func front_at(t: float) -> float:
	var v := _noise.get_noise_1d(t)
	if t < CALM_START:
		v = maxf(v, 0.3)
	return v

func _state_for(v: float, cold: bool) -> String:
	if v > cut_cloudy:
		return "clear"
	if v > cut_rain:
		return "cloudy"
	if v > cut_storm:
		return "snow" if cold else "rain"
	return "blizzard" if cold else "storm"

## The state at an absolute time, ignoring smoothing and overrides.
func state_at(t: float) -> String:
	var day := int(floor(t / float(day_night.day_length))) + 1
	return _state_for(front_at(t) + (HARD_WINTER_FRONT if hard_winter(day) else 0.0), is_cold_day(day))

func force(s: String) -> void:
	override = s
	snap()

## Jump every output straight to the current state's targets (on load, or
## when forcing a state).
func snap() -> void:
	_pick_state()
	var tg: Dictionary = TARGETS[state]
	clouds = tg.clouds
	precip = tg.precip
	wind = tg.wind
	light = tg.light
	fog = tg.fog
	warmth = tg.warmth + _cold_extra()
	ground_wet = 1.0 if state in ["rain", "storm"] else 0.0
	snow_cover = 0.7 if state in ["snow", "blizzard"] else (0.25 if cold_day else 0.0)

func _pick_state() -> void:
	if day_night == null:
		return
	cold_day = is_cold_day(day_night.day)
	var s := override
	if frozen and s.is_empty():
		s = "clear"
	if s.is_empty():
		s = _state_for(front_at(world_seconds()) + (HARD_WINTER_FRONT if hard_winter(day_night.day) else 0.0), cold_day)
	if s != state:
		state = s
		state_changed.emit(state)

func _process(delta: float) -> void:
	step(delta)

func step(dt: float) -> void:
	_pick_state()
	var tg: Dictionary = TARGETS[state]
	var k := dt / BLEND_SECONDS
	clouds = move_toward(clouds, tg.clouds, k)
	precip = move_toward(precip, tg.precip, k * 1.2)
	wind = move_toward(wind, tg.wind, k)
	light = move_toward(light, tg.light, k * 0.8)
	fog = move_toward(fog, tg.fog, k * 3.0)
	warmth = move_toward(warmth, tg.warmth + _cold_extra(), k * 20.0)
	# The ground soaks in a couple of minutes of rain and dries over ten.
	var raining := precip > 0.2 and not snowing_globally()
	ground_wet = move_toward(ground_wet, 1.0 if raining else 0.0, dt / (120.0 if raining else 600.0))
	# Snow settles over a few minutes and only melts on warm days.
	var snowing := precip > 0.2 and snowing_globally()
	if snowing:
		snow_cover = move_toward(snow_cover, 1.0, dt * precip / 180.0)
	elif not cold_day:
		snow_cover = move_toward(snow_cover, 0.0, dt / 480.0)
	flash = maxf(flash - dt * 6.0, 0.0)
	if state == "storm" and precip > 0.7:
		_strike_left -= dt
		if _strike_left <= 0.0:
			_strike_left = _rng.randf_range(7.0, 22.0)
			flash = 1.0
			lightning_count += 1

## Extra cold from the day: a cold day, and a hard winter on top.
func _cold_extra() -> float:
	if not cold_day:
		return 0.0
	return COLD_DAY_WARMTH + (HARD_WINTER_WARMTH if day_night != null and hard_winter(day_night.day) else 0.0)

func in_hard_winter() -> bool:
	return day_night != null and hard_winter(day_night.day)

## Extra warmth lost by someone out in a blizzard's wind (0 when sheltered or
## when it isn't blowing).
func blizzard_chill(sheltered: bool) -> float:
	if sheltered or state != "blizzard":
		return 0.0
	return BLIZZARD_CHILL * clampf(precip, 0.0, 1.0)

func snowing_globally() -> bool:
	return state in ["snow", "blizzard"]

## Whether precipitation at `pos` falls as snow (cold day or high up).
func snows_at(pos: Vector3) -> bool:
	return snowing_globally() or pos.y > snowline

## 0..1 rain intensity at `pos` (0 when it's snow there).
func rain_at(pos: Vector3) -> float:
	return 0.0 if snows_at(pos) else precip

## Air warmth change from the weather. Altitude snow makes the peaks colder
## still when precipitation is falling up there.
func warmth_at(pos: Vector3) -> float:
	var w := warmth
	if precip > 0.2 and pos.y > snowline and not snowing_globally():
		w -= 10.0 * precip
	return w

func label() -> String:
	var names := {"clear": "Clear", "cloudy": "Cloudy", "rain": "Rain", "storm": "Storm",
		"snow": "Snow", "blizzard": "Blizzard"}
	var s: String = names[state]
	if cold_day and state in ["clear", "cloudy"]:
		s += ", cold"
	if in_hard_winter():
		s += " (hard winter)"
	return s